OBD-II code family
Boost Bypass Control Faults (4 codes)
4 related fault descriptions. Use each full code and the exact vehicle service information to identify its circuit, monitored condition, and required tests.
Codes in this family
This is the complete published member list for this guide. Each code retains its own page; shared diagnostic context does not mean that every member has the same test or repair.
What these codes mean
P0033 concerns the bypass control circuit, P0034/P0035 identify low/high circuit conditions and P0039 describes range/performance. These are bypass-system faults; they should not be confused with boost-pressure sensor codes, wastegate faults or proof that the turbocharger itself has failed.
Identify the actual bypass device, actuator design, reporting controller and full code. A manufacturer can express specific fault types through suffixes: the covered Ford example relates P0034/P0035 to P0033 low/high subtypes. That example does not make all manufacturers’ labels or output stages interchangeable.
A bypass valve controls a flow path in the installed charging system. Its command, electrical input and physical response are different observations. A low/high condition does not directly describe low/high boost, and a range/performance result does not prove wiring is healthy. Do not assign a normal position, spring direction, sensor count or vacuum layout from the generic code.
Inspect cooled hoses and connectors where the actual procedure directs. Have compatible control, supply, feedback and mechanical tests performed before replacing a valve or turbocharger. Do not substitute a generic test lamp, apply battery power or force an electric actuator. Related pressure and engine-control faults can affect the test prerequisites.
After the confirmed repair, complete any specified setup and verification. A code that clears or a brief return of boost is not a complete performance check. Seek help for unsafe power loss, severe running problems, overheating or abnormal mechanical noise.
Identify the circuit on your vehicle
Match the full DTC, reporting module, and any failure-type suffix to the service information for your exact year, make, model, engine, and equipment. An identifier alone does not establish installed hardware count, location, connector pinout, or a universal measurement.
Where the manufacturer publishes its own meaning for this code, that is the one to work from — it describes the actual component on your vehicle, which the generic definition cannot. Keep the generic description for what it is good for: it tells you which subject area the standard assigned the code to, which is useful context when the two appear to disagree. If they do disagree, follow the manufacturer.